Respiration Flashcards
Define energy
Energy is the ability to do work
Define ATP
It is a phosphorylated nucleotide and is the universal energy currency
Define anabolic reactions
Biochemical reactions that use small molecules to synthesis larger ones
Define catabolic reactions
Biochemical reactions that break down larger molecules, via hydrolysis, to produce smaller ones
Define respiration
When energy stored in complex organic molecules is used to make ATP.
What does energy exist as?
Name 4 forms of energy.
Kinetic energy and potential energy
Heat, chemical, electrical and light
List 3 facts about energy
- Energy can not be created or destroyed but it can be transferred
- It’s measured in joules/kilojoules
- It has many forms
True or false.
Catabolic AND anabolic reactions occur in metabolic reactions
True
Name 7 metabolic processes that requires energy
- Active transport to move ions against their concentration gradient
- Secretion via exocytosis
- Endocytosis to move large molecules into a cell
- Anabolic reactions to produce proteins from amino acids, steroids from cholesterol and cellulose from beta glucose
- Replication of DNA/ organelles
- Movement, e.g. muscle contraction or organelles via microtubule motors
- Activation of chemicals, e.g. phosphorylating glucose in respiration
How are catabolic reactions useful in terms of temperature?
Sometimes the reactions release heat which keeps the enzymes, used in metabolic reactions, at their optimum temperature
Where does energy come from?
It comes from photoautotrophs when they photosynthesise in the presence of light to make complex organic molecules. These molecules have chemical potential energy and can be passed on to consumers and decomposers, they then release the energy and use it to phophorylate ADP to ATP.
Define phosphorylation
Adding an inorganic phosphate to a molecule
Describe ATP in detail
It’s a phosphorylated nucleotide and is a high-intermediate compound. ATP is found in both prokaryotes and eukaryotes. It consists of adenosine, which is adenine and a ribose sugar, and 3 phosphoryl groups. When hydrolysed to ADP and Pi, it releases 30.6 kj of energy per mol. It is the universal energy currency.
What does Adeonsine consist of?
What about adenosine monophosphate?
And Adenosine diphosphate?
Adenine and a ribose sugar
Adenosine and 1 phosphoryl group (AMP)
Adenosine and 2 phosphate molecules (ADP)
True or false
ATP is continually being hydrolysed but not resynthesised.
False
ATP is continually being hydrolysed AND resynthesised
What is the hydrolysis of ATP coupled with?
It is coupled with a synthesis reactions as the reaction can use the hydrolysed ATP as an immediate source of energy.
Are oxidation and reduction reactions, in terms of electrons, coupled with each other? Explain
Yes because as one molecule is oxidised (loses electrons), another molecule is reduced (gains those electrons).
What are the four stages of respiration?
Glycolysis, link reaction, Krebs cycle and oxidative phosphorylation
Briefly describe glycolysis
It occurs in the cytoplasm and can take place in aerobic and anaerobic conditions. Glucose, a 6 carbon sugar, is broken down into 2 molecules of pyruvate, a 3 carbon compound.
Briefly describe the link reaction
It occurs in the mitochondrial matrix and pyruvate is dehydrogenated and decarboxylated and then converted to acetate. It only occurs in aerobic conditions
Briefly describe the Krebs cycle
It occurs in the mitochondrial matrix and acetate is dehydrogenated and decarboxylated. It only occurs in aerobic conditions
Briefly describe oxidative phosphorylation
It occurs in the mitochondrial cristae (inner membrane) and ADP is phosphorylated to ATP via chemiosmosis. It only occurs in aerobic conditions
Why are coenzymes needed during respiration?
Because enzymes aren’t very good at oxidation and reduction reactions so coenzymes help the enzymes by becoming reduced which helps to catalyse the oxidation (in terms of hydrogen atoms) of substrates.
Give an example of a coenzyme and briefly describe its role
NAD and it gets reduced and carries the hydrogen atoms to the inner mitochondrial membrane where it’s then reoxidised and reused.
Describe NAD in detail
It’s an organic non-protein molecule which helps dehydrogenase enzymes carry out oxidation reactions. Its full name is nicotinamide adenine dinucleotide. NAD consists of 2 nucleotides, the nitrogenous base in one nucleotide is adenine and in the other it’s nicotinamide. They both have a ribose molecule and a phosphate molecule. Nicotinamide is the hydrogen acceptor and it accepts 2 hydrogen atoms at a time, this reduces NAD. NAD is required in the first 3 stages of respiration
Describe coenzyme A in detail
Coenzyme A is also called CoA. It consists of pantothenic acid, adenosine, 3 phosphoryl groups and cysteine (an amino acid). It carries ethanoate groups (acetate) made in the link reaction onto the Krebs cycle. It also carries the ethanoate groups made from fatty/amino acids to the Krebs cycle.
Define glycolysis
A metabolic pathway where each glucose molecule is broken down into 2 molecules of pyruvate in the cytoplasm. It can occur anaerobically and aerobically
Define hexose sugars
Sugars that contain six carbon atoms in each molecule
e.g. glucose
Define hydrolysis
Breaking down large molecules into smaller ones with the addition of water.
Define triose sugars
Sugars that contain the carbon atoms in each molecule
How many stages of glycolysis are there?
How many reactions are there?
Which coenzyme is involved?
4
10
NAD
Outline 4 things that occur during stage 1 of glycolysis
- An ATP molecule is hydrolysed and the released phosphate group phosphorylates the glucose molecule at carbon 6 to form glucose 6-phosphate
- Glucose 6-phosphate is changed to fructose 6-phosphate
- Another ATP is hydrolysed and the released phosphate group phosphorylates fructose 6-phosphate at carbon 1 to form fructose 1,6-bisphosphate. This reaction activates the hexose sugar
- The energy from the hydrolysed ATP activates the hexose sugar which prevents it from being transported out of the cell. Once activated, the phosphorylated molecule is called hexose 1,6-bisphosphate
How many ATP are used for each molecule of glucose in stage 1 of glycolysis?
2
Outline 1 thing that occurs during stage 2 of glycolysis
Hexose 1,6-bisphosphate is split into 2 molecules of triose phosphate. These are 3 carbon sugars with 1 phosphate group.
Outline 5 things that occur during stage 3 of glycolysis
- The triose phosphate molecules (aka the substrates) are oxidised meaning 2 hydrogen atoms are removed
- Dehydrogenase enzymes catalyse this
- NAD aids this as it’s the hydrogen acceptor. It accepts the hydrogen and becomes reduced NAD
- 2 molecules of NAD are reduced per glucose molecule
- 2 molecules of ATP are formed via substrate-level phosphorylation
Outline 2 things that occur during stage 4 of glycolysis
- 4 enzyme catalysed reactions convert each of the 2 triose phosphate molecules into a molecule of pyruvate, a 3 carbon compound.
- 2 molecules of ADP are phosphorylated to 2 ATP via substrate level phosphorylation
List the products of glycolysis and their amounts from 1 molecule of glucose. Describe how the products are needed for respiration.
There was a net gain of 2 ATP molecules as 4 were produced but 2 molecules were used to kick start the process.
2 molecules of reduced NAD were produced which will be used in oxidative phosphorylation
2 molecules of pyruvate were produced which will either be transported to the mitochondrial matrix for the link reaction or they will be converted to lactate/ethanol in the cytoplasm in anaerobic conditions.
Define mitochondria
An organelle that’s found in eukaryotic cells, it’s where the link reaction, kerbs cycle and oxidative phosphorylation occurs. These are the aerobic stages of respiration
Describe what the mitochondria consists of in detail
It has an inner and outer phospholipid membrane which makes up the envelope
The outer membrane is smooth whereas the inner membrane is folded into cristae, giving it a large surface area
Between the two membranes is the intermembrane space which is acidic
The inner membrane encloses a matrix which is a semi-rigid, gel like liquid containing proteins, lipids, mitochondrial DNA, mitochondrial ribosomes and enzymes
Describe the shape, size and distribution of mitochondria
Shape: The are rod shaped but can vary in size. Athletes have larger ones as they require more energy
Size: Between 2 and 5 um in length
Distribution: In athletes there are more mitochondria and they have more densely packed cristae meaning there are more ATP synthase enzymes and more ETCs. They’re more metabolically active
Can mitochondria be moved about in cells, explain
Yes, they can be moved around via the cytoskeleton but in nerve cells they are fixed in position near a site of high ATP demand
Where does the link reaction and the Krebs cycle occur?
In the mitochondrial matrix
What does the matrix consist of? 5 things
- Enzymes that catalyse reactions in the link reaction and Krebs cycle
- NAD
- Oxaloacetate which is a 4 carbon compound that accepts acetate from the link reaction
- Mitochondrial DNA which codes for mitochondrial enzymes and proteins
- Mitochondrial ribosomes which are structurally the same as prokaryote ribosomes, it’s where the proteins are assembled
What does the mitochondrial phospholipid outer layer contain?
It contains proteins that form channels or carriers and it contains enzymes.
List 3 things about the inner membrane.
- It has a different lipid composition from the outer membrane and is impermeable to small ions like hydrogen ions
- It’s folded into cristae giving it a large surface area
- Electron carriers and ATP synthase enzymes are embedded in it.
Describe what happens in an electron transport chain (ETC). 5 things in detail
- Electron carriers are enzymes that are associated with a cofactor which is a non-protein haem group containing an iron atom.
- The cofactors accept and donate electrons because the iron atoms can become reduced/oxidised by accepting/donating an electron to the next electron carrier.
- Cofactors are oxidoreductase enzymes because they are involved in oxidation and reduction reactions
- Some of the electron carriers have a coenzyme that pumps protons from the matrix to the intermembrane space. It actively does this using the energy released from the passage of electrons.
- The inner membrane is impermeable to protons so they accumulate in the intermembrane space which builds up a proton gradient
List 3 facts about ATP synthase enzymes
- They are large and protrude from the inner membrane into the matrix
- They are known as stalked particles
- They allow protons to pass through them
Define chemiosmosis and list 2 times when it occurs
Chemiosmosis is the flow of protons through an ATP synthase enzyme.
It occurs during oxidative phosphorylation and during the light dependent stage of photosynthesis
What is the point of chemiosmosis?
The flow powers the headpiece of the ATP synthase enzymes which phosphorylates ADP to ATP.
What enzyme and coenzyme is embedded into the inner membrane? (Other than ATP synthase enzymes)
Dehydrogenase enzymes and the coenzyme FAD.
When does FAD become reduced?
During the Krebs cycle
What happens to the hydrogen atoms once they are accepted by FAD?
They don’t get pumped into the intermembrane space like the other protons but they do get passed back into the matrix.
What is the full name for FAD and what does it consist of
Flavine adenine dinucleotide.
It consists of vitamin B, adenine, ribose and 2 phosphate groups.
Define the link reaction
A reaction that converts pyruvate to acetate and NAD is reduced
Define the Krebs cycle
A cycle that oxidises acetate to carbon dioxide. NAD and FAD are reduced and ATP is made via substrate level phosphorylation.
List the 4 stages of the link reaction
- Pyruvate dehydrogenase removes hydrogen atoms from pyruvate
- Two molecules of NAD accept them and become reduced
- Pyruvate decarboxylase removes a carboxyl group from pyruvate which eventually becomes carbon dioxide.
- Coenzyme A accepts acetate to become acetyl coenzyme A which carries acetate to the Krebs cycle
What indicates that NAD is oxidised?
If it has a plus by it: NAD+
What are the products of the link reaction and what are their qunatities per two molecules of pyruvate?
2 reduced NAD
2 acetyl coenzyme A
2 carbon dioxide
Why are two molecules of pyruvate in the link reaction?
Because 2 pyruvate molecules were made in glycolysis
How much ATP is made in the link reaction?
None
List the 6 stages of the Krebs cycle
- Acetate leaves conenzyme A (which can be reused) and joins with a 4 carbon compound called oxaloacetate which forms citrate
- Citrate is dehydrogenated (2 hydrogen atoms removed) and decarboxylated (1 molecule of CO2 removed) to form a 5 carbon compound. The hydrogen atoms reduce NAD
- The 5 carbon compound is dehyrdogenated and decarboxylated to form a 4 carbon compound. NAD is reduced again
- The 4 carbon compound is changed to a different 4 carbon compound, this reaction phosphorylates ADP to ATP via substrate level phosphorylation
- The 4 carbon compound is changed to another 4 carbon compound which reduces FAD as 2 hydrogen atoms are released
- The 4 carbon compound is dehydrogenated to create oxaloacetate and NAD is reduced.
What are the products of the Krebs cycles and what are their qunatities per 1 turn? What about per glucose molecule
2 carbon dioxide 1 ATP 3 reduced NAD 1 reduced FAD Per glucose molecule which creates 2 acetate: 6 reduced NAD, 2 reduced FAD, 4 CO2 and 2 ATP
How many turns of the Krebs cycle is there for 1 molecule of acetate? How many turns of the cycle is there per molecule of glucose?
1 turn per acetate
2 turns per glucose as 2 pyruvate were produced from glycolysis meaning two molecules of acetate are produced
Does the link reaction and Krebs cycle occur in aerobic or anaerobic conditions? Is oxygen actually used?
Aerobic
No
Can food substances, other than glucose, be used for respiration?
Yes
What is a source of acetate, other than pyruvate?
Can amino acids be used in the Krebs cycle?
Fatty acids that can be broken down
Yes
Define oxidative phosphorylation
The formation of ATP by phosphorylating ADP in the presence of oxygen. Oxygen is the final electron acceptor.
What does the electron transport chain consist of?
It consists of a series of proteins that are embedded in the inner mitochondrial membrane
What happens just before oxidative phosphorylation occurs?
Reduced NAD and reduced FAD are reoxidised and the hydrogen atoms are split into protons and electrons. The electrons are accepted by the first protein in the ETC.
What is the first protein/electron carrier in the ETC called? (It accepts electrons from the reoxidised NAD) It has 2 names, name both.
NADH-coenzyme Q reductase
NADH dehydrogenase
How many protein complexes are there in the ETC? Which complex accepts electrons from the reoxidised NAD?
4
Protein complex I
How are the electrons passed between protein complexes in the ETC? What does this release?
The electrons are passed along the ETC via redox reactions. This releases energy
As electrons are passed along the ETC, energy is released. How is this energy used?
It is used to pump protons (H+) from the matrix to the intermembrane space. Coenzymes associated with protein complex I, III and IV pump them. The remaining energy is lost via heat
Why are protons pumped into the intermembrane space?
They’re pumped into the intermembrane space because it builds up a proton gradient, a pH gradient and an electrochemical gradient. This means that there is a lot of potential energy in the intermembrane space. This energy can be used to create ATP
What happens once there is a high proton gradient in the intermembrane space? Why can’t the protons diffuse through the lipid part of the inner membrane back into the matrix
Chemiosmosis occurs meaning that the protons flow down their concentration gradient through a protein channel that’s associated with ATP synthase and back into the matrix
How does oxidative phosphorylation occur?
It occurs because the protons drive the rotation of the headpiece of ATP synthase which phosphorylates ADP to ATP.
What happens to the electrons when they reach protein complex IV?
What protein donates the electrons to oxygen in protein complex IV?
The electrons are passed to the final electron acceptor which is oxygen
Cytochrome oxidase
Once oxygen has accepted the electrons, what happens?
It accepts the protons from FAD or protons that are diffusing down their concentration gradient, this reduces oxygen to form H2O.
Energy is released when water is formed in oxidative phosphorylation. How is this energy used?
This energy is used to pump more protons back into the intermembrane space so more ATP can be synthesised.
What happens to the reduced FAD from the Krebs cycle?
Where does this happen?
What happens to the reduced NAD from other stages in respiration?
It’s reoxidised to release protons and electrons. The electrons enter the ETC at protein complex II whereas the protons bind with oxygen and electrons to produce water.
This happens at protein complex II
Reduced NAD is reoxidised at protein complex I and the protein accepts the protons and electrons
What is another term for hydrogen ions?
Protons
How many molecules of ATP are produced per reduced NAD?
Work out how many molecules of ATP are created during respiration. This is the yield.
2.6
10 reduced NADs are produced so 10 X 2.6= 26 ATP
2 ATP are made in glycolysis and Krebs so 26 + 4= 30 ATP
How many molecules of NAD and FAD are reduced during respiration per 1 molecule of glucose?
NAD: 2 in glycolysis, 2 in the link reaction and 6 in the Krebs cycle so 10 altogether.
FAD: 2 in the Krebs cycle
Why is the total yield of ATP in respiration rarely achieved? 3 reasons
Whatis the efficiency of ATP production? (percentage)
- Some protons leak across the mitochondrial membrane, reducing the number of protons for chemiosmosis
- Some ATP produced is used to actively transport pyruvate into the mitochondrial matrix from the cytoplasm
- Some ATP is used to transport reduced NAD from the cytoplasm (made during glycolysis) to the mitochondria.
32%
What was Peter Mitchell’s theory?
It was the theory of chemiosmosis
Give an example of an energy transducing membrane.
The inner mitochondrial membrane
What is the force of flow called in the inner mitochondrial membrane? It drives the production of ATP.
The proton motive force
Describe an experiment completed that aimed to find out the contents of the mitochondria. Give lots of detail. 7 things
The mitochondria was isolated via placing it in a solution with a very low water potential.
This caused the outer membrane to rupture which released the contents of the intermembrane space, the mitochondria is now called a mitoblast.
The mitoblasts were then treated with strong detergent which ruptured the inner membrane, releasing the contents of the matrix
From this, they discovered where various enzymes are in the mitochondria, where the link reaction and Krebs cycle takes place and where the ETC is embedded
They also found out that the mitoblasts didn’t produce ATP meaning the intermembrane space is involved in oxidative phosphorylation
The found out that when the stalked particles (ATP synthase enzymes) were removed, no ATP was made
Also ATP wasn’t made in the presence of oligomycin as it blocked the proton channels
What is the potential difference across the inner mitochondrial membrane?
Which side is more negatively charged?
Which side has a lower pH?
-200 mV
Matrix is more negatively charged
Intermembrane space has a lower pH
Why does the intermembrane space have a small volume?
What does the outer membrane contain?
To maximise the concentration of hydrogen ions
It contains transport proteins for pyruvate, oxygen, carbon dioxide and ATP
Define anaerobic respiration
The release of energy from substrates (glucose) in the absence of oxygen
Why can’t the electron transport chain function without oxygen present?
What processes does this stop?
In anaerobic conditions, what process of respiration creates ATP?
Because oxygen is needed as it’s the final electron acceptor
The link reaction, the Krebs cycle and oxidative phosphorylation
Glycolysis but only small amounts of ATP are made
Why does NAD need to be reoxidised in anaerobic conditions?
Because then glycolysis can occur and create small amounts of ATP
What are the two pathways to reoxidise NAD in anaerobic conditions?
Which organisms use which pathway?
Do these pathways produce ATP
Ethanol fermentation and lactate fermentation
Fungi (yeast) uses ethanol fermentation
Animals use lactate fermentation
No
When does lactate fermentation occur?
Describe the process
It occurs during vigorous activity (escaping from a predator) when the demand for ATP is high but the concentration of oxygen is low.
- Pyruvate is the hydrogen acceptor and it accepts hydrogen atoms from reduced NAD (produced in glycolysis), this reduces pyruvate to lactate.
- This reoxidises NAD (the purpose of the pathway) meaning its available to accept hydrogen atoms in glycolysis again. Lactate dehydrogenase catalyses this.
- Glycolysis can continue to produce sufficient ATP to sustain muscle contraction
Where does aerobic respiration occur?
Once lactate has been made via lactate fermentation, what happens to it?
In contracting muscles
It is taken away from the muscles via the blood and is then transported to the liver. If oxygen is then available, it can be converted back to pyruvate or glucose.
What causes muscle fatigue?
The reduction of pH which reduces enzyme activity. The pH is reduced because of a build up of lactate that isn’t counteracted by buffers.
Describe the anaerobic pathway for reoxidising NAD in yeast cells. 3 things
The anaerobic pathway is alcohol fermentation.
Each pyruvate molecule is decarboxylated via pyruvate decarboxylase with thiamine disphosphate (a coenzyme) bound to it to produce ethanal
Ethanal then accepts hydrogen atoms from reduced NAD, reoxidising NAD and reducing ethanal to ethanol. Ethanol dehydrogenase catalyses this
The reoxidised NAD can now re-enter glycolysis
Why can’t animals use the alcohol fermentation pathway?
Because they don’t have pyruvate decarboxylase which is an essential enzyme for the pathway to occur.
Define facultative anaerobes and give an example of one.
An organism that can live without oxygen
Yeast cells are facultative anaerobes
What concentration of ethanol in a yeast cell kills it?
If the concentration of ethanol reaches 15% the yeast dies
Is the rate of growth faster for yeast in aerobic or anaerobic conditions?
In aerobic conditions the rate of growth is faster
Briefly describe the brewing process for yeast
The yeast are firstly grown in aerobic conditions so that they grow quickly and they are then placed in anaerobic conditions to undergo alcohol fermentation
Define respiratory substrate
An organic substance that can be used for respiration
Define mole
The gram molecular mass of a substance. For example there is 180 g of glucose in one mole of glucose.
Define respiratory quotient
The ratio of the volume of carbon dioxide produced compared to the volume of oxygen used in a set period of time.
Finish the sentence:
The more hydrogen atoms there are in a respiratory substrate…
…the more ATP produced when the substrate is respired
Finish the sentence:
The more hydrogen atoms per mol of respiratory substrate…
…the more oxygen required to respire that substance
What is the general formula for a carbohydrate
Cn(H20)n
What mammalian cells can only use glucose as a respiratory substrate?
Brain cells and red blood cells
What is the chief respiratory substrate?
Glucose
What do animals store glucose as?
What about plants?
Animals store glucose as glycogen
Plants store glucose as starch
What can glycogen or starch be hydrolysed into?
They can be hydrolysed into glucose for respiration
Give 3 examples of monosaccharides.
Glucose, galactose and fructose. Galactose and fructose can be converted to glucose for respiration
What is the maximum energy yield for glucose?
And how many kJ does it take to produce 1 mol of ATP?
Theoretically, how many mol of ATP will 1 mol of glucose make?
What is the actual yield and efficiency?
How is the energy lost?
2870 kJ mol-1 30.6 kJ 94 mol of ATP Actual yield is 30 mol of ATP Efficiency is 32% The energy is lost via heat to maintain body temperature
After an amino acid is deaminated, what happens to the rest of the molecule?
It’s converted into glycogen or fat which can be stored and later respired
What happens to the protein from muscle when an organism is undergoing starvation or prolonged exercise? 3 things
What is the benefit of using proteins for respiration?
The protein is hydrolysed to amino acids which can then be respired
The protein can be converted to pyruvate or acetate and can then be carried to the Krebs cycle
The protein can enter the Krebs cycle directly
More hydrogen atoms per mol are accepted by NAD (3 NADH) so more energy is created, compared to equivalent masses of carbs
What is an important respiratory substrate for muscles?
Lipids
How can lipids be respired?
Can fatty acids be respired?
Triglycerides can be hydrolysed by lipase to fatty acids and glycerol. Glycerol can then be converted glucose and respired
No
Describe the structure of fatty acids.
Why would they be good for respiration?
They are long-chain hydrocarbons with a carboxylic acid group
They would be good for respiration because they contain many hydrogen atoms so they are a good source of protons
How can fatty acids be converted so that they can be used in respiration?
The fatty acids can combine with CoA using the energy from the hydrolysis of ATP to AMP (and 2 Pi groups)
The fatty acid-CoA complex can then be transported to the mitochondrial matrix and be broken down into 2-carbon acetyl groups attached to CoA
The breakdown pathway is called the beta-oxidation pathway and it forms reduced NAD and FAD
The acetyl groups are then released from CoA and they enter the Krebs cycle, each acetate molecule reduces 3 NAD, 1 FAD and produces 1 ATP.
This means large amounts of ATP are produced during oxidative phosphorylation
What is the mean energy value (aka amount of hydrogen atoms) for carbohydrates in respiration?
What about proteins?
And lipids?
15.8 kJ g-1
17 kJ g-1
39.4 kJ g-1
